Question

I have 4 arrays and use array_multisort to sort them all at the same time relative to one another.
Problem is, in the first array, there can be empty values and I want to put them at the end, not the beginning.

Example : http://codepad.org/V6TjCsS5

Is there a way to:

• Pass a custom function to array_multisort
  or
• Sort the first array with a custom function then use the result order to sort the other arrays
  or
• Use a certain argument with array_multisort to achieve what I want

Thank you very much

Answer 1

Unfortunately none of the approaches your propose is possible, which means you have to take another step back and look for alternatives. I am assuming you want a normal ascending sort, with the explicit exception that empty elements (which you be “smallest”) need to be considered as “largest”.

Option 1: Manually rearrange elements after sorting

Do your array_multisort as usual, and then make the modifications you require:

// $arr1, $arr2 etc have been sorted with array_multisort
while(reset($arr1) == '') {
    $k = key($arr1);
    unset($arr1[$k]); // remove empty element from beginning of array
    $arr1[$k] = ''; // add it to end of array
    // and now do the same for $arr2
    $v = reset($arr2);
    $k = key($arr2);
    unset($arr2[$k]);
    $arr2[$k] = $v;
    // the same for $arr3, etc
}

You can pull out part of the code in a function to make this prettier:

function shift_and_push(&$arr) {
    $v = reset($arr);
    $k = key($arr);
    unset($arr[$k]);
    $arr[$k] = $v;
}

Option 2: Condense everything inside one array so you can use usort

The idea here is to pull all your arrays into one so you can specify the comparison function by using usort:

$allArrays = array_map(function() { return func_get_args(); },
                       $array1, $array2 /* , as many arrays as you want */);

You can now sort:

// writing this as a free function so that it looks presentable
function cmp($row1, $row2) {
    // $row1[0] is the item in your first array, etc
    if($row1[0] == $row2[0]) {
        return 0;
    }
    else if($row1[0] == '') {
        return 1;
    }
    else if($row2[0] == '') {
        return -1;
    }

    return $row1[0] < $row2[0] ? -1 : 1;
}

usort($allArrays, "cmp");

At this point you are left with an array, each element (row) of which is an array. The first elements of each are what was originally inside $array1, second elements are what was in $array2, etc. By placing those elements inside “rows”, we have managed to keep the sort order among all your original arrays synchronized.